Why Don’t Pregnant Women Tip Over?

A University of Texas researcher has been awarded the tongue-in-cheek “IgNobel” prize for answering this age-old question: “Why don’t pregnant women tip over?”

Liz Shapiro, a UT anthropologist, and two fellow researchers at Harvard won the prize on Thursday for their 2007 study. The IgNoble prize is dedicated to “achievements that first make people laugh, and then make them think.”

The first human ancestor walked upright about 6 million years ago, but the first pregnant, upright-walking female very likely could have tipped over when she tried to walk … or at the very least had a really bad back ache.

It’s not really surprising how pregnant women avoid tipping over: they lean back. What Shapiro and the other researchers learned was that evolution has made that (somewhat) easier for women. According to UT, the researchers studied 19 pregnant women, and they discovered that a woman’s lumbar, or lower back, curve extends across three vertebrae. In men, it extends across two. The joints between the vertebrae also are larger in females and angled differently from those of males to better support the extra weight. The researchers say the extra back support evolved about 2 million years ago, and likely came about as a direct result of walking upright.

“This is something that certainly half the population has thought about,” says Marc Abrahams, editor of the Harvard-based Annals of Improbable Research, which gives out the IgNobles. “Every woman who is, has been or has ever contemplated the possibility of being pregnant has thought about this but never had an answer until now.”